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Bob McDavitt's ideas for sailing weather around the South pacific

26 June 2022

Bobgram 26June

Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the
patterned world.

Compiled Sunday 26 June 2022

The Winter Solstice migration
A series of active fronts across the Tasman Sea NZ area for the first half
of June delayed departure for many yachts in NZ wanting to get to the
tropics. Then, around the shortest day/winter solstice last Tuesday, the
weather pattern became OK for departure and a large cluster of yachts set
forth.

Passage Planning
A regular yachtie around the Pacific is Richard West on SV Legacy. He is
currently in New Caledonia and looking at a good weather pattern for sailing
to Goldstone in Queensland. He has generously decided to take time out and
record the thinking process he uses to evaluate when to depart and what may
be encountered on this voyage. These videos are useful for anyway doing
weather passage planning and goes thru the tools that are available. His
comments on how to use the new boat handling parameters now available of
Predictwind are also very useful. This new hydrodynamic tool uses the wave
polars of your vessel to compute the three axes of motion, what I call the
roll, heave and slam of the waves.

You can find these videos at
twoatsea.com/weather-planning-for-passages-video-series/

He also looks at the steepness factor as mentioned in one of my previous
blogs metbob.wordpress.com/2019/02/17/bob-blog-17-feb/
The Steepness factor was introduced by Dr. Dilip Barua at
widecanvas.weebly.com/nature/waves-height-period-and-length

TROPICS
CELIA is travelling west northwest in the northeast tropical Pacific. Areas
of potential development are around the Philippines and central America.

WEATHER ZONES

SPCZ=South Pacific ConvL1ergence zone and STR (Sub tropical ridge).
The SPCZ stretches across the Coral Sea to northern Vanuatu to Fatuna.
A convergence zone/trough is expected to trave east across New Caledonia on
Tuesday and Fiji on Wednesday then travel further east.
It looks ok to sail from Tahiti to Tonga this week.

HIGHS and LOWS
High H1 east of Chathams is expected to travel slowly along 40S this week
maintaining steady trade winds Low L1 is expected to form in the trough that
crossed NZ on Saturday and travel SE on western side of H1.
Low L2 is expected to form on the northwest side of a trough crossing South
Island on Monday.
Another trough is expected to cross the South Island on Thursday and the
North Island on Friday followed by a cold southerly.
HIGH H2 is expected to form over NSW on Tuesday and move slowly east across
the Tasman Sea reaching central NZ early next week.
Wait until after L2 for an Ok pattern to travel north from NZ or west from
Noumea.
. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If you would like more detail for your voyage, then check metbob.com to see
what I offer.
Or Facebook at /www.facebook.com/metbobnz/ Weathergram with graphics is at
metbob.wordpress.com (subscribe/unsubscribe at bottom).
Weathergram archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt 64277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

19 June 2022

Bob Blog 19 June

Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the
patterned world.
Compiled Sunday 19 June 2022

The State of the ENSO
La Nina is lingering but has weakened
Since last August the Pacific trade winds have been stronger than normal and
dragging sun-warmed sea to the west, encouraging upwelling of cooler deeper
water around the Galapagos. This "La Nina" episode shifts the subtropical
ridge poleward
However, the Tasman Sea has recently had a series of lows and these this
week affecting the area east of NZ.

The Atmosphere:
ENSO = El Nino/Southern Oscillation. The main parameter we watch from the
atmosphere is the Southern Oscillation Index SOI (30 day running mean) as it
sums up the whole weather pattern over the South Pacific into one number. It
is based on the standardized difference in the barometer readings between
Tahiti and Darwin, in other words it counts the average number of isobars
between them on the weather map. When the SOI is more than plus one
(standard deviation from its mean) for more than a month we call it a LA
NINA event, and when it stays more than minus one, we call it an EL NINO
event.
SOI can be seen at
www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekly
The weekly SOI was as high as over +2 in May (making this May the 2nd equal
highest year on record since 1876) and is relaxing during June but still
well over +1.

The Ocean:
The sea surface temperatures in the equatorial eastern Pacific Ocean are the
action centre for ENSO (El Nino Southern Oscillation). This area has been
blue (cooler than normal) for LA NINA shows clearly in a time-longitude plot
from http://www.cpc.ncep.noaa.gov shown here. The rippled pattern is an
artifact of west-moving eddies. There seems to have been a relation during
the last month
These cool waters are surrounded by a ring of warmer waters across central
North Pacific, around Indonesia and then across central south Pacific. A
warmer than normal Tasman Sea has been producing extra lightning for NZ
recently.

According to the International Research Institute of the Climate Prediction
Centre,
at iri.columbia.edu/our-expertise/climate/forecasts/enso/current/, reviewing
all of the different models for forecasting the future of this La Nina, it
is expected to strengthen in a few months and then weaken by end of the
year.


Impact on South Pacific
Trade winds are expected to be reliable between Galapagos and Marquesas.
Having the subtropical ridge further south than normal during winter should
keep the winter lows south of normal as well, but this hasn't been the case
in June.

TROPICS
TBLAS formed south of Acapulco and is travelling west.
CELIA formed offshore of El Salvador and is travelling west northwest.

WEATHER ZONES
The SPCZ stretches across the Coral Sea to northern Vanuatu to Samoa.
A convergence zone/trough is expected to trave east across Fiji on
Monday/Tuesday and reach the Cooks by end of the week.
The best route this week from Tahiti westwards this week seems to be the
northern route, and may need to deviate around the trough

HIGHS and LOWS
The upper trough from last week is now east of NZ and expected to form L1
that deepens as it travels SE.
L2 has also formed between New Caledonia and New Zealand in tandem with L1
and is expected to travel of to the ESE then East.

H1 is the surface sign of a long wave ridge and expected to travel northeast
across central NZ by mid-week.
Between H1 and L1 , ice-chilled air is expected to be strongly shovelled
northwards onto eastern NZ

Weather pattern looks OK this week for crossing the Tasman Sea.
For those wanting to sail from NZ to the tropics, this may be done on the
backside of L2 once the swell has eased.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If you would like more detail for your voyage, then check metbob.com to see
what I offer.
Or Facebook at /www.facebook.com/metbobnz/
Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe
at bottom).
Weathergram archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt 64277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

12 June 2022

Bob Blog 12 June

Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the
patterned world.
Compiled Sunday 12 June 2022

Other versions of the Beaufort scale
THE SHAKERS AND THE BREAKERS scale
Here is a simple matrix for determining wind speed in km/hr by watching a
tree
Item move shake break
Leaves 10 40 70
Twigs 20 50 80
Branches 30 60 90
Tree topples at over 100kph

For example if the twigs are shaking , wind is 50kph. 50kph is the speed
of a strong wind, and when this is happens we should observe its effect
around us and use this as training for future comparisons.

And on a more whimsical side here is a modern version of the Beaufort scale
for cruising sailors from
https://weather.mailasail.com/Franks-Weather/Historical-And-Contemporay-Vers
ions-Of-Beaufort-Scales

Helmsman's version Crew's version
0-1 Drifting conditions Boredom
2 Set large sail to catch wind. Mild pleasure.
3 Large headsail and full mainsail Pleasure
4 Reduce headsail and mainsail Great pleasure
5 Reduce headsail and reef mainsail Delight
6 Ditto Delight tinged with anxiety
7 Reefed mainsail and small jib Anxiety tinged with fear
8 Deep reefed mainsail Fear tinged with terror
9 Set storm jib and trysail Great terror
10 Survival conditions Panic

TROPICS
The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical
Cyclone Potential is from www.ssd.noaa.gov/PS/TROP/TCFP/index.html
Early last week Cyclone ALEX brought an early start to the 2022 Atlantic
Cyclone season.
AT present there is a strong potential that a low which may soon form south
of Acapulco and develop into a cyclone that ] drifts west for a few days.

WEATHER ZONES
SPCZ=South Pacific ConvL1ergence zone and STR (Sub tropical ridge).
The SPCZ stretches from PNG/Coral Sea to north of Vanuatu and to Tuvalu.
Another convergence zone stretches from Coral Sea to New Caledonia to the
SE. A low L2is expected to form on this near New Caledonia by Thursday and
then deepen as it goes SE this weekend. The STR should spend the week along
30S allowing a High H1 to slowly travel east. A good time for traveling west
from Tahiti.

The best route this week from Tahiti westwards this week seems to be the
northern route.

HIGHS and LOWS
An upper trough has been forming over the Tasman Sea last week and has bred
L1. L1 is expected this week to deepen as it travel across NZ and further
east. It is bringing wintery conditions to NZ and drawing in air from off
the ice shelf of the Southern Ocean. In a few weeks it may weaken the LA
NINA and that may usher change to weather patterns across the entire
Pacific.

For those wanting to cross the Tasman, wait a few days for the swells around
L1 to ease.
For those wanting to sail from NZ to the tropics L2 may be a challenge this
weekend, so check that out.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If you would like more detail for your voyage, then check metbob.com to see
what I offer.
Or Facebook at /www.facebook.com/metbobnz/ Weathergram with graphics is at
metbob.wordpress.com (subscribe/unsubscribe at bottom).
Weathergram archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt 64277762212

04 June 2022

Bob Blog 5 June

Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the
patterned world.
Compiled Sunday 05 June 2022

REVIEW OF THE LAST MONTH (May 2022)
Sea Surface temperature anomalies from
psl.noaa.gov/map/clim/sst.shtml

Sea surface temperature anomolies: the cool eddies along the eastern
equatorial Pacific that signify LA Nina are relaxing. The surrounding C
shaped ring of warm water across north Pacific Indonesia and South Pacific,
and warm zones across the south Tasman Sea and off South Africa are more
intense than last month.

To see how the annual weather cycle and the seasons are working out, we can
check the average isobar maps for past 30 days and their anomaly from
psl.noaa.gov/map/images/fnl/slp_30b.fnl.html
The subtropical ridge in the northern Hemisphere has weakened since last
month.
The anomaly map shows that the lows around Australia are wider than last
month , and there is a high area between Australia and Antarctica.
Zooming into the NZ area, These maps show that the subtropical ridge has
sifted north and weakened, as shown by the 1015 over Australia/NZ, and the
fading of the 1020 off South America.

TROPICS
A few days before the nominal start of the North Pacific/Atlantic cyclone
season AGATHA made land fall over SW Mexico as a hurricane. It weakened as
it travelled over land, and its remnants redeveloping into damaging rain
over Cuba yesterday. This system is just a tropical depression for now,
labelled ONE or AL01, but may soon earn a new name as it is forecast to
bring damaging conditions to Florida tomorrow.

WEATHER ZONES
SPCZ=South Pacific ConvL1ergence zone.
The SPCZ stretches from PNG/Coral sea to Northern Vanuatu is looking rather
weak this week.
Convergence zone forming around Niue area is expected to travel east to
Tahiti area by late in the week
The best route this week from Tahiti westwards this week seems to be the
northern route.

HIGHS and LOWS
High H1 was over NZ today/Saturday and is travelling off to the east
Low L1 is expected to form south of Tahiti by mid-week.
Low L2 is expected to travel along 45 to 50S from Tasmania to NZ by mid-week
and may be followed by another similar Low. Associated troughs are likely to
cross NZ on Sunday, Tuesday and Friday/Saturday, making it difficult to find
a good day to depart from Opua.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If you would like more detail for your voyage, then check metbob.com to see
what I offer.
Or Facebook at /www.facebook.com/metbobnz/
Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe
at bottom).
Weathergram archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt 64277762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

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